1. Field of the Invention
The present invention relates to an electronic device and a method of producing the device, and more particularly, to an electronic device in which a silicon nitride insulating film is laid on a conductive member formed on the surface of an insulating substrate, and a method of producing the device.
2. Description of the Related Art
As an example of a conventional electronic device, a thin-film transistor (referred to as a TFT hereinafter) used to drive an active matrix liquid crystal display device shown in FIG. 5 will be described.
FIG. 6 is a sectional view taken along line A-A' shown in FIG. 5 and conceptually illustrates a TFT array. Since FIG. 6 is a conceptual view, the dimensions therein are different from those of an actual device.
Referring to FIG. 6, numerals 9 and 10 respectively denote a gate electrode (wiring pattern) and a gate wire (wiring pattern) patterned on a substrate 5. An insulating film 3 includes a gate insulating film 3a and an interlayer insulating film 3b at the intersection of wires.
Numerals 11, 12 and 13 respectively denote a source electrode, a source wire and a drain electrode.
A silicon nitride thin film is frequently used as the gate insulating film 3a and the interlayer insulating film 3b at the intersection of multilevel metal wires of the TFT array.
In a desirable composition of the silicon nitride thin film, the element ratio of silicon to nitrogen is approximately 3 to 4 and a trace quantity of hydrogen is contained therein to stabilize the quality thereof. Such insulating layer is mainly formed in plasma enhanced chemical vapor deposition (referred to as PECV-D hereinafter). As a material gas, silane-nitrogen, silane-ammonia-nitrogen, silane-ammonia-hydrogen, silane-nitrogen-hydrogen, and silane-ammonia-nitrogen-hydrogen gases are normally used.
However, in an electronic device like such TFT using silicon nitride insulating films as the gate insulating film 3a and the interlayer insulating film 3b at the intersection of multilevel wires, an electrical short circuit sometimes occurs between the gate electrode 9, the gate wire 10 and wires formed through the insulating film (the source wire 12, the source electrode 11 and so on). More particularly, the probability such short circuit will occur is very high in a highly integrated or large-area substrate. Such short circuit may occur during use or the production process of an ultimate product. If the short circuit occurs during use of the ultimate product, the reliability of the product is lowered. Furthermore, a short circuit occurring during the production process lowers the yield. For example, dielectric breakdown sometimes occurs between the source wire 12 and the gate wire 10 or the gate electrode 9 during a photoresist process for forming contact holes and so on after the formation of the source wire 12 and so on.
Considering that these problems result from the existence of pinholes in the insulating film, Japanese Laid-open Patent No. 58-190042 attempts to solve the problems by adopting a so-called multilayered insulating film structure in which a non-doped amorphous silicon layer is laid on the intersection of a gate wire and a source wire. However, since this technique is used on the assumption that the insulating layer will not have a single layer structure, but a multilayered insulating film structure, it is hard to avoid complication of the production process.
Accordingly, an electronic device such as a TFT of a single-layer structure which is excellent in the dielectric characteristics and capable of being easily produced is desired.
Particularly, since the electronic device is now frequently used in harsh environments, it is desired that the break-down voltage of the insulating film be more than 100 V. Furthermore, it is desirable from the viewpoint of miniaturization of the electronic device that the thickness of the insulating film be limited to less than 500 nm, preferably, 200 to 400 nm. Therefore, an electronic device having a thin insulating film, which has a thickness of approximately 200 nm and a break-down voltage of more than 100 V, is desired.
No electronic device which satisfies such desire has been developed up to now.
A silicon nitride thin film is frequently used as an insulating film in an electronic device, for example, an insulating film 103 at the intersection of multilevel metal wires of a TFT array used to drive an active matrix liquid crystal display device shown in FIGS. 12 and 13. Such film is mainly formed in the PECV-D method, and silane-nitrogen, silane-ammonia/nitrogen, silane-ammonia-hydrogen, silane-nitrogen-hydrogen and silane-ammonia-nitrogen-hydrogen gases are well known as a material gas of the film. The film is deposited at a temperature of more than 300.degree. C. to stabilize the quality thereof. This temperature is several tens of degrees higher than the temperature at which an amorphous silicon layer frequently used in the electronic device is formed. When a similar insulating film is formed in sputtering, argon of more than 0.50 Pa is put into an atmosphere.
However, the silicon nitride thin film formed in the PECV-D or sputtering method using the above mixed gas has more pinholes and lower break-down voltage than an oxidized film formed by high temperature oxidization of silicon. Even if the silicon nitride thin film is used in an electronic device, the single layer structure of the film makes it difficult to obtain the necessary break-down voltage. Therefore, in the TFT array shown in FIGS. 12 and 13, the necessary break-down voltage is obtained from a multilayered film formed by adding another film at the intersection of the multilevel metal wires. This complicates the structure and production process of the film.
Furthermore, since the temperature for depositing an insulating film in the PECV-D method is high, many foreign particles are generated from the inner wall of a film forming device in the forming operation, and these sometimes have a bad influence on the quality of the film.
Still furthermore, in an electronic device such as a TFT having an amorphous silicon film in direct contact with an insulating film, since the insulating film and the amorphous silicon film are different in film depositing temperature, it is necessary to increase or decrease the temperature of a substrate so as to achieve the depositing temperature of one of the films after forming the other film, and such adjustment of temperature takes a long time.